The invention relates to a combination of a solenoid device having an electrical coil and an energization control circuit therefor, and in particular, to a solenoid valve apparatus including a solenoid valve for opening and closing a fluid passage, as one of solenoid devices, and an energization control circuit for controlling the energization of the electrical coil of the solenoid valve. A solenoid valve apparatus of the kind described may be used to control the air intake of a negative pressure controlled engine which is applied to a negative pressure actuator driving a throttle valve of an engine onboard a vehicle.
Referring to FIG. 4 initially which illustrates a conventional solenoid valve in section, it includes a non-magnetic bobbin 12 which may be molded from synthetic resin and around which an electrical coil 3 is disposed. A stator core 5 of a magnetizable material is inserted into the bobbin 12 and is fixed in place. A fluid passage communicating with a third fluid port 11 is formed in alignment with the axis of the core 5. A movable plunger 6 of a magnetizable material is disposed to the left of the core 5, and is urged to the left by a coiled compression spring 8 which abuts against the core 5 at its one end and against the core 6 at its other end. A first valve element 13 is fixedly mounted on the left end face of the core 6 while a second, annular valve element 14 is fixedly mounted on the right end face of the core 6. The coil bobbin 12 is integrally formed with a port member 2 as a continuous portion thereof, in which a first and a second fluid port 9, 10 are defined. The right end of the first fluid port 9 is disposed opposite to the valve element 13 and is closed thereby. The outside of the coil 3 is covered by a casing member 4. A yoke 7 of a magnetizable material has a left end 7a and a right end 7b, both of which are folded. The left end 7a bears against both the port member 2 and an inwardly turned, left end flange of the casing member 4 while the right end 7b bears against the right end face of the stator core 5. A connector pin 15 is fixedly mounted in the bobbin 12 and is electrically connected to the coil 3, and extends through a connector receiver 4a which is integral with the casing member 4.
When the coil 3 is energized, there is produced a path for the magnetic flux extending through the stator core 5, the movable core 6, the yoke 7 and returning to the stator core 5, whereby the movable core 6 is attracted to the stator core 5, whereupon the first valve element 13 moves away from the right end opening of the port 9 and to the right while the second valve element 14 abuts against the left end face of the stator core 5. In this manner, the third port 11 is closed while the first port 9 communicates with the second port 10. When the coil 3 is deenergized, the first port 9 is closed by the valve element 13 while the second port 10 communicates with the third port 11, as shown in FIG. 4. A solenoid valve of the kind described is disclosed, for example, in U.S. Pat. No. 4,326,696 issued to Eiji Ishikawa et al.
When a solenoid valve of the kind described is used to control the running of a vehicle at a constant speed, for example, the third port 11 is connected to the intake manifold, not shown, of an engine onboard a vehicle, or a source of negative pressure, the first port 9 communicates with the atmosphere, and the second port 6 is connected to a negative pressure actuator (not shown) which drives a throttle valve. When the coil 3 remains deenergized, a negative pressure is applied to the actuator while the atmospheric pressure is applied to the actuator when the coil 3 is energized. When the coil 3 is pulsed at a given duty cycle, a pressure which depends on the duty cycle is applied to the actuator.
The engine on the vehicle is rendered operative upon turning an ignition switch on and is rendered inoperative upon turning the ignition switch off. When the ignition switch is turned off, the temperature of a fuel within a carburetor rises in response to the engine interrupting to operate, whereby a vapor of fuel is generated to increase the concentration of a gas mixture within the carburetor to an excessively high value. Such an excessively high concentration of the gas mixture causes a poor starting condition for the engine to operate for the next time. To cope with this problem, as illustrated in FIG. 5, the carburetor is provided with an outer vent OTV, which is connected to a canister CNT through a solenoid valve EMV, the energization of which is controlled by a control circuit CCT to maintain the valve EMV energized for a given time interval T upon turning the ignition switch off to thereby introduce the fuel vapor within the carburetor to the canister CNT. In this manner, the concentration of the gas mixture within the carburetor is lowered to provide an improved subsequent starting condition. When the solenoid valve 1 shown in FIG. 4 is used as the solenoid valve EMV, the first port 9 is connected to the vent OTV while the second port 10 is connected to the canister CNT. Since it is sufficient that the valve EMV operates as a switching valve, the third port 11 may be omitted from connection. When a conventional control circuit CCT is employed, the valve EMV is energized for a given time interval T upon turning the ignition switch off, so that the voltage from a power source or a battery of the vehicle is maintained applied to the control circuit CCT if the ignition switch is off, causing a power dissipation by the electrical circuit of the control circuit CCT to cause a reduction in the battery voltage. Accordingly, it is preferred that the control circuit CCT be constructed in a manner such that the power dissipation is minimized after the time interval T upon turning the ignition switch off.
In any event, in the prior art practice, the solenoid valve 1 is mounted within an engine room of the vehicle, and the connector receiver 4a and the connector pin 15 of the valve 1 are engaged by a female connector connected to one end of a electrical lead (not shown). The lead extends to the interior of the vehicle so that it may be connected to an energization control circuit located within a dashboard of the vehicle. An electrical current of a relatively high level which is sufficient to drive the movable core 6 passes through the lead. Within the engine room, oscillations are applied to the valve 1, whereby the connection between the female connector (not shown) connected to the electrical lead may be temporarily disengaged from the connector pin 15 within the connector receiver 4a as a result of such oscillations, giving rise to electrical sparks which damage the area of contact between the female connector and the connector pin 15 to cause a poor electrical interconnection. Since the lead which carries the energizing current of the coil is relatively heavy, it requires a certain space for its disposition from the engine room to the interior of the vehicle. Such disposition of the electrical lead may be difficult in some instances.